Missing Malaysia Airlines flight MH370 and search in Indian Ocean
A P-3K2 Orion search aircraft lands at the RAAF Base Pearce near PerthReuters

The investigation into Malaysia Airlines Flight MH370 is now classified as a "criminal investigation", according to new reports.

The Wall Street Journal has reported that the missing Boeing 777-200ER carrying 239 passengers and crew is now being investigated for criminal activity, citing the Malaysian police chief.

A series of updates linked to the newspaper's Twitter feed quotes Khalid Abu Bakar as saying police have taken over 170 statements for the ongoing probe. According to the inspector general of police, authorities continue to interview more people and even cargo and food served on the plane were being investigated in case of sabotage.

Yet Bakar has also cautioned that "we may not even know the real cause" of the mystery of what happened to MH370, after the investigation has concluded. He added that any investigation finding would not be released at this time as it may impact a later prosecution.

He also said that the investigation into captain Zaharie Ahmad Shah's flight simulator is still inconclusive, as authorities are awaiting an expert's report.

Malaysian authorities handed over flight simulator hard drives to US authorities, including the FBI, after discovering information had been deleted.

Bakar said the investigation could "go on and on and on" as authorities "have to clear every little thing", Malaysia's Bernama news agency has reported.

He added that police had "cleared" all the passengers of the four key areas being investigated: hijacking, sabotage and psychological and personal problems.

Meanwhile, Malaysian Prime Minister Najib Razak will head to Australia for talks on the search. He is due to arrive in Perth, western Australian, on Wednesday evening and will visit the Joint Agency Coordination Centre (JACC) where the southern Indian Ocean search is being led.

Najib will meet Australian Prime Minister Tony Abbott, and Angus Houston, the retired air chief marshal, who is leading the JACC.

The British submarine HMS Tireless has also arrived in the southern Indian Ocean, which will soon be joined by Royal Navy ship HMS Echo. The private jet of film director Peter Jackson has also joined the search.

Meanwhile, lawyers have already begun contacting the families of those on board about possible multimillion-dollar settlements in US courts over the incident. The New York Times reported: "The rush is on to secure compensation for families of the flight's 227 passengers, about two-thirds of whom are Chinese. Insurance companies [in China] have already made payments to some relatives.

It continued: "On top of that, the families can expect to receive compensation from Malaysia Airlines because of guarantees in an international treaty. They can also opt to sue the airline for more damages, or sue Boeing or a component manufacturer. Any lawsuit could take years to conclude."